Tyndall effect

The Tyndall effect is when light is scattered by particles of matter in its path. It makes a beam of light visible by lighting the particles.

Under the Tyndall effect, the longer-wavelength light is more transmitted while the shorter-wavelength light is more reflected by scattering. In effect, blue light is scattered much more strongly than red light.

The blue of a clear sky, and the blue of blue eyes is caused by the Tyndall effect, not by a pigment.